I am currently using a cfc and I do like it. My only issue is that I can't get wort temps below 65 as my incoming water is around 63. Has any one out there tried a pre chiller for a cfc, and if so how well did it work.
Pre-chillers work, but in my experience, not great.
I think you'd be better off running your wort through a post chiller, rather than trying to cool your ground water which is blasting through at high speed.
Then again though, I'd be thrilled to see anything in the 60's with my tap water. If I can get it to 75, that's pretty good. Lately I've been forced to just let my fermenters chill overnight before I pitch yeast.
If you have a pump run the tap water into your HLT and put a couple of ice blocks in it (they're cheap). Run the HLT output into the pump, then out of the pump through the chiller, and out of the chiller into the sink drain. Slow your flow down so that your wort coming out is the desired temp. Slow the water flow so you don't waste the ice. I have done this and gotten wort output temps in the high 50s. I do this after I have cooled to within about ten degrees of summer tap water which is about 70-ish.
If you don't have a pump then I think a post chiller would probably be best.